Use export_mp4_dataset to create training data

[Mona77]

Hi

Thank you so much for sharing your great work!
I'm trying to train a similar model on PointOdyssey dataset.

1. What is the difference between train.tar.gz, train.tar.gz.partaa and train.tar.gz.partXX and so on?
2. Should I run export_mp4_dataset.py for each of mod and its corresponding training chunk in this code:

    mod = 'aa' # copy from dev repo; crop_size=(256x384), S=36
    mod = 'ab' # allow more OOB, by updating threshs to 64; export at 384,512; output 256; export as long as we have N//2
    mod = 'ac' # N=128
    mod = 'ad' # put more info into name; also print rtime
    mod = 'ae' # allow trajs to go behind camera during S

3. Should the resize tuple depends on crop value in this line?